This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Modern society is greatly dependent on the use of hydrocarbons for fuels and chemical feedstocks. Hydrocarbons are generally found in subsurface rock formations that can be termed “reservoirs.” Removing hydrocarbons from the reservoirs depends on numerous physical properties of the rock formations, such as the permeability of the rock containing the hydrocarbons, the ability of the hydrocarbons to flow through the rock formations, and the proportion of hydrocarbons present, among others.
As many newer reservoirs are located in challenging environments, such as in deep oceanic environments, production methods increasingly rely on long (˜300 m) and ultra-long (˜3,000 m) open hole, horizontal well (OHHW) completions. These horizontal completions can be drilled from a single platform or rig to reach numerous locations in a reservoir. Long and ultra-long OHHW completions may present unique challenges associated with construction, completion, stimulation, or production. This may be due to a variety of factors, including the length of the well, variations in the subterranean formations that may be experienced along the length of the well, and variations in the reservoir fluids that may be encountered along the length of the well. Because of these and other factors, construction, completion, stimulation, or production operations may be improved by controlling a flow of fluid between the subterranean formation and the well.
To assist in flow control, wells are often completed with a variety of flow control devices and fluid flow conduits, including casing strings, production liner assemblies, packers, and uniformity enhancing devices, such as inflow control devices (ICDs). Casing strings and/or production liner assemblies may provide a conduit for the flow of fluid between the subterranean formation and a surface region. Packers may be placed within a well to inhibit fluid flow and isolate sections of the well. ICDs can provide a restriction to a flow of production fluids from the formation into the well, such as from the wellbore into the production liner. The restriction may be constant or may vary with a flow rate of the reservoir fluid through the ICD. As an illustrative example, a pressure drop across the ICD may increase significantly as a flow rate of reservoir fluid increases through the ICD. This has the effect of equalizing the inflow from different intervals. Further, the equalization helps to prevent the production of unwanted fluid such as water that might otherwise dominate the production. The ICDs can be adjusted to promote or hinder inflow from certain intervals.
After drilling, the production rates of the completed wells can be further improved by stimulation. Stimulation is a process by which the flow of hydrocarbons between a formation and a wellbore is improved. This can be performed by any number of techniques, such as fracturing a rock surrounding the wellbore with a high pressure fluid, injecting a surfactant into a reservoir, or injecting steam to lower the viscosity of the hydrocarbons. One technique uses an acid injection through the wellbore into the surrounding formation, which can remove drilling debris from the wellbore and increase flow from the formation, for example, by forming wormholes into the formation. Wormholes are small holes or cracks formed by acid attack on certain types of rock.
However, stimulating open hole, horizontal well (OHHW) completions, especially the distal portions, is very challenging due to the length of the completions. Acid placement is important for a successful acid stimulation. However, acid will generally flow into areas of least resistance, e.g., into areas of high permeability. This is opposed to the main objective of the matrix treatment, which is to increase the productivity of low permeability zones.
One approach to stimulation is to simply pump an acid through the ICDs. However, this approach only injects the acid in the vicinity of the ICDs and may fail to stimulate the formation away from the ICDs. Further, the ICDs restrict the rate of acid that can be injected. Even if the acid migrates along the annulus, recent research has indicated that it may be important for effective stimulation to achieve radial impingement of the acid on the formation achievable only by high injection rates. In addition, sizing the ICDs to work for both acid injection and hydrocarbon production can be problematic.
Another approach to stimulation is to pre-drill the liner with holes and then perform the stimulation using coiled tubing with an acid jetting Bottom Hole Assembly (BHA). By moving the coiled tubing during acidizing, essentially the entire production interval can be treated. However, this approach may not be feasible for longer wells, for example, greater than about 6,100 m (about 20,000 ft.) because of the difficulty in running coiled tubing in such wells. Also, coiled tubing typically limits acid pumping rates to <5 bbl/min where rates as great as 50 bbl/min may be desired for improved performance and reduced job time. Furthermore, pre-drilled holes preclude the use of ICDs, since the inflow would enter through the holes. Creating the perforations and renting the coiled tubing is also very expensive and may be difficult in remote locations.
Numerous mechanical and chemical diversion methods have been developed to place acid in the desired areas of the formation around the well. Mechanical methods make use of various bridge plugs, packers, ball sealers and their combination. Chemical diversion utilizes various chemical systems designed to make acid interact with the formation in the area of interest. Chemical systems used for diversion can include salt granules, waxes, foam, viscous pills, and the like.
For example, one approach to stimulating long horizontal wells is to use special ports that can be opened by dropping activation balls. The balls typically land in a sleeve that shears and opens ports in the liner. Then the acid can be pumped through the ports. This system is commonly used for multi-zone fracture stimulation of shale gas wells. However, the use of such a system would preclude the use of ICDs, since the hydrocarbons would enter the well through the open ports.
U.S. Pat. No. 7,748,460, to Themig, discloses a method and apparatus for wellbore fluid treatment. An apparatus includes a tubing string assembly for fluid treatment of a wellbore. The tubing string assembly includes substantially pressure holding closures spaced along the tubing string, which each close at least one port through the tubing string wall. The closures are openable by a sleeve drivable through the tubing string inner bore.
U.S. Patent Publication No. 2009/0151925 by Richards, et al., discloses a “well screen inflow control device with check valve flow controls.” The well screen assembly includes a filter portion and a flow control device which varies a resistance to flow of fluid in response to a change in velocity of the fluid. Another well screen assembly includes a filter portion and a flow resistance device which decreases a resistance to flow of fluid in response to a predetermined stimulus applied from a remote location. Yet another well screen assembly includes a filter portion and a valve including an actuator having a piston which displaces in response to a pressure differential to thereby selectively permit and prevent flow of fluid through the valve.
The disclosures described above can target locations in a well for contact with a stimulation fluid. However, both describe complex methods and or assemblies that can be expensive to implement and may be difficult to install or use. Simpler techniques for targeted stimulation of certain zones are desirable.